The present invention relates generally to fabrication of integrated circuits, and more particularly, to a method for reducing dimensions beyond photolithography limitations during a patterning process by selectively patterning and trimming each of a plurality of layers of different hardmask materials in a successive sequence.
Referring to FIG. 1, for fabrication of an integrated circuit structure, a layer of target material 102 is deposited on a semiconductor substrate 104. For example, for formation of a gate of a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), the layer of target material 102 may be comprised of polysilicon. For patterning and etching the layer of target material 102 to form the integrated circuit structure, a photoresist structure 106 has been patterned and etched from a layer of photoresist material in a photolithography process as known to one of ordinary skill in the art of integrated circuit fabrication. The photoresist structure 106 has a length 108 and a height 110.
Referring to FIGS. 1 and 2, any exposed region of the layer of target material 102 is etched away to form a target structure 112 of the target material remaining under the photoresist structure 106. Thus, the target structure 112 has the same length 108 as that of the photoresist structure 106.
A long-recognized important objective in the constant advancement of monolithic IC (Integrated Circuit) technology is the scaling-down of IC dimensions. Such scaling-down of IC dimensions reduces area capacitance and is critical to obtaining higher speed performance of integrated circuits. Moreover, reducing the area of an IC die leads to higher yield in IC fabrication. Such advantages are a driving force to constantly scale down IC dimensions.
In FIGS. 1 and 2, to scale down the length of the target structure 112, the length 108 of the photoresist structure 106 is scaled down during the photolithography process for forming the photoresist structure 106. However, photolithography processes for forming the photoresist structure 106 have limitations for a minimum length, as known to one of ordinary skill in the art of integrated circuit fabrication. Nevertheless, dimensions that are smaller than the minimum length achievable with photolithography process limitations are desired as integrated circuit devices are scaled down further.
Referring to FIGS. 1 and 3, for achieving such smaller dimensions than achievable with photolithography process limitations, after the photoresist structure 106 is formed to the minimum length possible given photolithography process limitations, the photoresist structure 106 is trimmed to reduce the original length 108 of the photoresist structure 106 by a trim length 114 using a photoresist trimming process as known to one of ordinary skill in the art of integrated circuit fabrication. During such a photoresist trimming process, the dimensions of the photoresist structure 106 are reduced by the trim length 114 at the two sides and at the top of the photoresist structure 106 as illustrated in FIG. 3. In this manner, the target structure formed from etching away any exposed region of layer of the target material 102 has the scaled down length of the photoresist structure 106 of FIG. 3.
During the photoresist trimming process, the two sides and the top of the photoresist structure 106 are trimmed by the substantially same trim length 114. Thus, with the photoresist trimming process of the prior art, the minimum length of the photoresist structure 106 is limited by the height 110 of the photoresist layer forming the original photoresist structure 106.
Furthermore, referring to FIG. 4, even if the photoresist structure 106 having a small length were formed with a relatively thick photoresist layer, the aspect ratio (defined as the height to the length) of the photoresist structure 106 is high. Because photoresist material is a malleable material as known to one of ordinary skill in the art of integrated circuit fabrication, the photoresist structure 106 having high aspect ratio is likely to deform in shape by bending over.
Referring to FIG. 5, a hardmask structure 116 having a length 118 and comprised of a hardmask material (such as silicon nitride for example) that is not as malleable as photoresist material may be formed to pattern the layer of target material 102. The dimensions of the hardmask structure 116 may be further scaled down in a hardmask trimming process as known to one of ordinary skill in the art of integrated circuit fabrication. However, because the dimensions of the hardmask structure 116 would be trimmed at both the side surfaces and the top surface of the hardmask structure 116 during the hardmask trimming process, the minimum length of the hardmask structure 116 is limited by the original height of the hardmask structure 116, similar to the photoresist structure 106.
Furthermore, referring to FIG. 5, when the hardmask structure 116 is comprised of a dielectric material (such as silicon nitride for example), having a large height for a large trim length, the top corners of the hardmask structure 116 become rounded during the hardmask trimming process to form the hardmask structure 116, as known to one of ordinary skill in the art of integrated circuit fabrication. With such rounded top corners of the hardmask structure 116, the thickness of the hardmask structure 116 tapers to be smaller at the sides of the hardmask structure 116 down toward the layer of target material 102. Referring to FIGS. 5 and 6, during etching of the target material 102 to form the target structure 112, the portion of the hardmask structure 116 having the smaller thickness at the sides of the hardmask structure 116 down toward the layer of target material 102 may etch away to result in an undesired smaller length 120 of the hardmask structure 116 and the target structure 112. Thus, the length of the target structure 112 is more difficult to predict and control when using the single hardmask structure 116.
Despite such disadvantages of trimming the single photoresist structure 106 of the prior art (as illustrated in FIGS. 1, 2, 3, and 4) or the single hardmask structure 116 of the prior art (as illustrated in FIGS. 5 and 6), the dimensions of the target structure are desired to be further scaled down.
Thus, a mechanism is desired for scaling down the dimensions of the target structure beyond photolithography process limitations without the disadvantages of trimming the single photoresist structure 106 of the prior art or the single hardmask structure 116 of the prior art.
Accordingly, in a general aspect of the present invention, a plurality of layers of different hardmask materials having relatively small thickness are selectively patterned and trimmed in a successive sequence to achieve dimensions beyond photolithography process limitations.
In one embodiment of the present invention, in a method for patterning a layer of target material on a semiconductor substrate, the method includes a step of depositing a layer of first hardmask material on the layer of target material. The first hardmask material is different from the target material. A layer of second hardmask material is deposited on the layer of first hardmask material, and the second hardmask material is different from the first hardmask material. A layer of patterning material is deposited on the layer of second hardmask material. The layer of patterning material is patterned and etched such that a patterned structure of the patterning material remains on the second layer of second hardmask material.
Any exposed region of the layer of second hardmask material is etched using a first etching reactant such that a second hardmask structure is formed from the second hardmask material remaining under the patterned structure and on the layer of first hardmask material. The first etching reactant substantially does not etch the layer of first hardmask material, and the second hardmask structure has a second mask length. The patterned structure is then removed from the second hardmask structure.
The second hardmask structure is trimmed with a first trimming reactant in a hardmask trimming process to reduce the second mask length by a second trim length at each side of the second hardmask structure. The first trimming reactant substantially does not etch the layer of first hardmask material.
Any exposed region of the layer of first hardmask material is etched using a second etching reactant such that a first hardmask structure is formed from the first hardmask material remaining under the second hardmask structure and on the layer of target material. The second etching reactant substantially does not etch the second hardmask material and the target material, and the first hardmask structure has a first mask length. The second hark mask structure is then removed from the first hardmask structure.
The first hardmask structure is trimmed with a second trimming reactant in a hardmask trimming process to reduce the first mask length by a first trim length at each side of first second hardmask structure. The second trimming reactant substantially does not etch the target material. Any exposed region of the target material is etched using a third etching reactant such that a target structure is formed from the target material remaining under the first hardmask structure. The third etching reactant substantially does not etch the first hardmask material. The first hardmask structure is then removed from the target structure.
The present invention may be used to particular advantage when the layer of first hardmask material and the layer of second hardmask material have a relatively small thickness is a range of from about 100 xc3x85 to about 250 xc3x85 to prevent rounding of the top corners of the first hardmask structure and the second hardmask structure.
In this manner, because a plurality of layers of different hardmask materials are selectively patterned and trimmed in a successive sequence, each of the layers of different hardmask materials may have relatively small thickness to prevent rounding of the top corners of the hardmask structures formed with patterning of each of the hardmask materials. In addition, the length dimension of the target structure is further scaled down with patterning and trimming of each of the plurality of layers of different hardmask as materials.
These and other features and advantages of the present invention will be better understood by considering the following detailed description of the invention which is presented with the attached drawings.